Expandable interbody fusion device

ABSTRACT

An apparatus and method is provided for interbody fusion including distracting, in a given direction, and supporting opposing vertebral bodies. A plurality of wafers are consecutively inserted between the vertebral bodies to create a column of wafers. The column of wafers is oriented between the vertebral bodies so as to expand in the given direction as the wafers are consecutively added to the column.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/628,707, filed on Feb. 23, 2015, now U.S. Pat. No. 9,655,743, whichis a continuation of U.S. application Ser. No. 14/027,421, filed on Sep.16, 2013, now U.S. Pat. No. 8,974,464, which is a continuation of U.S.application Ser. No. 13/176,830, filed on Jul. 6, 2011, now U.S. Pat.No. 8,535,353, which is a continuation of U.S. application Ser. No.11/867,746, filed on Oct. 5, 2007, now U.S. Pat. No. 8,123,755, which isa divisional of U.S. application Ser. No. 10/623,957, filed on Jul. 21,2003, now U.S. Pat. No. 7,311,713, which is a continuation of U.S.application Ser. No. 09/872,905, filed on Jun. 1, 2001, now U.S. Pat.No. 6,595,998, which claims the benefit of priority to U.S. ProvisionalApplication No. 60/274,372, filed on Mar. 8, 2001, the disclosures ofwhich are incorporated by reference herein.

FIELD OF THE INVENTION

The present invention involves the field of surgery, and particularlysurgical instruments and methods of using the same.

BACKGROUND OF THE INVENTION

A variety of physical conditions involve two tissue surfaces that, fortreatment of the condition, need to be distracted from one another andthen supported away from one another. Such distraction may be to gainexposure to select tissue structures, to apply a therapeutic pressure toselect tissues, to return tissue structures to their anatomic positionand form, or in some cases to deliver a drug or growth factor to alter,influence or deter further growth of select tissues. Depending on thecondition being treated, the tissue surfaces may be opposed orcontiguous and may be bone, skin, soft tissue, or a combination thereof.An optimal treatment method includes distracting and supporting thetissue surfaces simultaneously.

A minimally invasive distraction and support device would havesignificant application in orthopaedic surgical procedures, includingacute and elective procedures to treat bone fractures and degenerativechanges of the skeletal system and including vertebral compressionfractures, interbody fusion, vertebral disc augmentation or replacement,and other compression fractures including, but not limited to tibialplateau compression fractures, calcaneous compression fractures, distaltibia fractures, distal radius (wrist) fractures, crushed or fracturedorbit and orthopaedic oncology. Further, a minimally invasivedistraction and support device would have application in non-orthopaedicsurgical procedures in plastic surgery (for example facialreconstruction), gastrointestinal surgery and urological surgery (forexample the treatment of incontinence).

Vertebral Compression Fractures

A vertebral compression fracture is a crushing injury to one or morevertebrae. Vertebral fractures are generally associated withosteoporosis (the “brittle bone” disease), metastasis, and/or trauma.Osteoporosis reduces bone density, thereby weakening bones andpredisposing them to fracture.

The osteoporosis-weakened bones can collapse during normal activity. Insevere cases of osteoporosis, actions as simple as bending forward canbe enough to cause a vertebral compression fracture. Vertebralcompression fractures are the most common type of osteoporotic fracturesaccording to the National Institute of Health. The mechanism of thesefractures is one of flexion with axial compression where even minorevents cause damage to the weak bone. While the fractures may healwithout intervention, the crushed bone may fail to heal adequately.Moreover, if the bones are allowed to heal on their own, the spine willbe deformed to the extent the vertebrae were compressed by the fracture.Spinal deformity may lead to breathing and gastrointestinalcomplications, and adverse loading of adjacent vertebrae.

Vertebral fractures happen most frequently at the thoracolumbarjunction, with a relatively normal distribution of fractures around thispoint. Vertebral fractures can permanently alter the shape and strengthof the spine. Commonly, they cause loss of height and a humped back.This disorder (called kyphosis or “dowager's hump”) is an exaggerationof the spinal curve that causes the shoulders to slump forward and thetop of the back to look enlarged and humped. In severe cases, the body'scenter of mass is moved further away from the spine resulting inincreased bending moment on the spine and increased loading ofindividual vertebrae.

Another contributing factor to vertebral fractures is metastaticdisease. When cancer cells spread to the spine, the cancer may causedestruction of part of the vertebra, weakening and predisposing the boneto fracture.

Osteoporosis and metastatic disease are common root causes leading tovertebral fractures, but trauma to healthy vertebrae also causes minorto severe fractures. Such trauma may result from a fall, a forcefuljump, a car accident, or any event that stresses the spine past itsbreaking point. The resulting fractures typically are compressionfractures or burst fractures.

Vertebral fractures can occur without pain. However, they often cause asevere “band-like” pain that radiates from the spine around both sidesof the body. It is commonly believed that the source of acute pain incompression fractures is the result of instability at the fracture site,allowing motion that irritates nerves in and around the vertebrae.

Until recently, treatment of vertebral compression fractures hasconsisted of conservative measures including rest, analgesics, dietary,and medical regimens to restore bone density or prevent further boneloss, avoidance of injury, and bracing. Unfortunately, the typicalpatient is an elderly person who generally does not tolerate extendedbed rest well. As a result, minimally invasive surgical methods fortreating vertebral compression fractures have recently been introducedand are gaining popularity.

One technique used to treat vertebral compression fractures is injectionof bone filler into the fractured vertebral body. This procedure iscommonly referred to as percutaneous vertebroplasty. Vertebroplastyinvolves injecting bone filler (for example, bone cement) into thecollapsed vertebra to stabilize and strengthen the crushed bone.

In vertebroplasty, physicians typically use one of two surgicalapproaches to access thoracic and lumbar vertebral bodies:transpedicular or extrapedicular. The transpedicular approach involvesthe placement of a needle or wire through the pedicle into the vertebralbody, and the physician may choose to use either a unilateral access orbilateral transpedicular approach. The second approach, theextra-pedicular technique, involves an entry point through theposterolateral corner of the vertebral body. The needle entry point istypically 8 cm to 12 cm lateral of the mid-sagittal plane, with the skinincision typically closer to 8 cm in the proximal spine and generallycloser to 12 cm in the distal spine. In general, one cannula is placedto fill the vertebral body with the extra-pedicular approach.

Regardless of the surgical approach, the physician generally places asmall diameter guide wire or needle along the path intended for the bonefiller delivery needle. The guide wire is advanced into the vertebralbody under fluoroscopic guidance to the delivery point within thevertebrae. The access channel into the vertebra may be enlarged toaccommodate the delivery tube. In some cases, the delivery tube isplaced directly and forms its own opening. In other cases, an accesscannula is placed over the guide wire and advanced into the vertebralbody. After placement, the cannula is replaced with the delivery tube,which is passed over the guide pin. In both cases, a hollow needle orsimilar tube is placed into the vertebral body and used to deliver thebone filler into the vertebra.

In this procedure, lower viscosities and higher pressures tend todisperse the bone filler throughout the vertebral body. However, suchconditions dramatically increase the risk of bone filler extravasationfrom the vertebral body. The transpedicular approach requires use of arelatively small needle (generally 11 gauge or smaller). In contrast,the extrapedicular approach provides sufficient room to accommodate alarger needle (up to 6 mm internal diameter in the lumbar region andlower thoracic regions). In general, the small diameter needle requiredfor a transpedicular approach necessitates injecting the bone filler ina more liquid (less viscous) state. Further, the pressure required toflow bone filler through a small gauge needle is relatively high. Thedifficulty of controlling or stopping bone filler flow into injurysensitive areas increases as the required pressure increases. The largerneedle used in the extrapedicular approach allows injection of bonefiller in a thicker, more controllable viscous state. Therefore, manyphysicians now advocate the extrapedicular approach so that the bonefiller may be delivered through a larger cannula under lower pressure.

Caution must be taken to prevent extravasation, with the greatestattention given to preventing posterior extravasation because it maycause spinal cord trauma. Physicians typically use fluoroscopic imagingto monitor bone filler propagation and to avoid flow into areas ofcritical concern. If a foraminal leak results, the patient may requiresurgical decompression and/or suffer paralysis.

Kyphoplasty is a modified vertebral fracture treatment that uses one ortwo balloons, similar to angioplasty balloons, to attempt to reduce thefracture and restore vertebral height prior to injecting the bonefiller. Two balloons are typically introduced into the vertebra viabilateral transpedicular cannulae. The balloons are inflated to reducethe fracture. After the balloon(s) is deflated and removed, leaving arelatively empty cavity, bone cement is injected into the vertebra. Intheory, inflation of the balloons restores vertebral height. However, itis difficult to consistently attain meaningful height restoration. Itappears the inconsistent results are due, in part, to the manner inwhich the balloon expands in a compressible media and the structuralorientation of the trabecular bone within the vertebra.

Tibial Plateau Compression Fractures

A tibial plateau fracture is a crushing injury to one or both of thetibial condyles resulting in a depression in the articular surface ofthe condyle. In conjunction with the compression fracture, there may bea splitting fracture of the tibial plateau. Appropriate treatment forcompression fractures depends on the severity of the fracture. Minimallydisplaced compression fractures may be stabilized in a cast or bracewithout surgical intervention. More severely displaced compression withor without displacement fractures are treated via open reduction andinternal fixation.

Typically, the underside of the compression fracture is accessed eitherthrough a window cut (a relatively small resection) into the side of thetibia or by opening or displacing a splitting fracture. A bone elevatoris then used to reduce the fracture and align the articular surface ofthe tibial condyle. A fluoroscope or arthroscope may be used tovisualize and confirm the reduction. Bone filler is placed into thecavity under the reduced compression fracture to maintain the reduction.If a window was cut into the side of the tibia, the window is packedwith graft material and may be secured with a bone plate. If a splittingfracture was opened to gain access, then the fracture is reduced and maybe stabilized with bone screws, bone plate and screws, or a buttressplate and screws. (Both of these methods are very invasive and requireextensive rehabilitation.)

Spinal Interbody Fusion

Spinal fusion is most frequently indicated to treat chronic back painassociated with instability or degenerative disc disease that has notresponded to less invasive treatments. Fusion is also prescribed totreat trauma and congenital deformities. Spinal fusion involves removalof the spinal disc and fusing or joining the two adjacent vertebrae. Theprimary objective for patients suffering from instability is to diminishthe patient's pain by reducing spinal motion.

Spinal fusions are generally categorized into two large groups:instrumented and non-instrumented. In non-instrumented procedures, thephysician removes tissue from the unstable disc space and fills it withsome form of bone graft that facilitates the fusion of the two adjacentvertebral bodies. Instrumented procedures are similar tonon-instrumented procedures, except that implants (generally metallic)are also applied to further stabilize the vertebrae and improve thelikelihood of fusion.

Conventional instrumented procedures generally utilize plates, rods,hooks, and/or pedicle screws through various surgical approaches. Theseconventional implants are secured to the vertebral bodies that are beingfused. Interbody fusion devices were introduced in the 1990's as a lessinvasive surgical alternative, although interbody devices areincreasingly being used in conjunction with pedicle screws. Interbodydevices are implanted into the disc space to restore the normal discspacing, utilizing tension in the annulus to stabilize the fusion unit.Interbody fusion provides a large area of the vertebral end plate forestablishing bony fusion, a viable blood supply from the decorticatedend plates, and dynamic compressive loading of the graft site. Theinterbody devices are generally filled with a bone filler to facilitatefusion. Interbody devices can be categorized in three primary groups:spinal fusion cages, which are available in a variety of shapesincluding rectangular, round-faced, and lordotic; allograft bone dowelsand wedges (which are also available in various shapes); and titaniummesh (although titanium mesh is not itself a structural spacer).

Interbody fusion is typically completed through a posterior, ananterior, or a lateral intertransverse approach. Each of thesetechniques has limitations. Lumbar interbody fusion presents achallenging surgical procedure and relatively high pseudoarthrosisrates. As a result, this approach is increasingly combined withadditional internal fixation devices such as pedicle screw fixation.

In all interbody surgical approaches, a relatively large opening is madein the annulus. The nuclear material is removed and the end plates aredecorticated to facilitate bony fusion. Overall, the use of interbodydevices has resulted in mixed clinical outcomes. Placement of a fixedheight device presents challenges in proper tensioning of the annulus.For these and other reasons, there is concern over long-term stabilityof interbody devices and fusion mass.

SUMMARY OF THE INVENTION

The invention provides a combination of a temporary or long termimplantable device and instrumentation to place the device, in whichtissue surfaces are distracted along an axis to enable access to thespace between the tissues. Generally, the invention provides wafers forstacking upon one another to provide an axially extending column todistract and support tissue surfaces. While a primary use of theinvention is to reduce and stabilize vertebral compression fractures,the invention may be used in any situation where it is desirable todistract two tissue surfaces. The tissue may be bone, skin, soft tissue,or combinations thereof. Further, the surfaces may be opposed surfacesof contiguous elements or surfaces of opposed elements. Thus, theinvention may be used to treat vertebral compression fractures, forreplacement of vertebral discs, as an interbody fusion device, wedgeopening high tibial osteotomy, tibial tuberosity elevation, as well asfor treating other compression fractures including, but not limited totibia plateau fractures, calcaneous, distal tibial fractures, or distalradius (wrist) fractures. The invention may also be used for restoringthe floor of the orbit, for elevating soft tissue in cosmeticapplications, or in incontinence applications as a urethral restrictor.Alternately, the invention may be used in similar veterinaryapplications.

The Distraction Device

The terms “vertical”, “up”, etc., are occasionally used herein for easeof understanding, and these terms should be taken in reference to thevertebrae of a standing patient. Thus, “vertical” refers generally tothe axis of the spine. We may also utilize mutually perpendicular “X”,“Y” and “Z” axes to describe configurations and movement, with theZ-axis being the axis of the column of wafers, that is, the direction inwhich this column grows as wafers are added sequentially to it. TheX-axis refers to the axis extending generally in the direction ofmovement of each wafer as it is advanced to a position beneath apreceding wafer, and the Y-axis is perpendicular to both the X- andZ-axes. The wafers are sometimes described with reference to permitteddegrees of freedom or restraint when they are placed in a column. Itshould be understood that these permitted degrees of freedom orrestraint refer to the permitted or restrained movement of one waferwith respect to an adjacent wafer along one or more of the three axes,and the permitted or restrained rotation between adjacent wafers aboutone or more of these axes.

The distraction device includes a plurality of stackable wafers designedfor insertion between tissue surfaces to form a column. The wafer columnis assembled in vivo to provide a distraction force as well as supportand stabilization of the distracted tissue. Preferably, the wafers placedistraction force in one direction only and thus provide directionaldistraction. The distraction device may be permanently implanted, inwhich case the wafer column may be used alone or in conjunction with abone filler material. Alternately, the distraction device may be usedtemporarily to manipulate tissues and then removed.

In use, the wafers are preferably stacked between two tissue surfaces asthey are implanted, thereby distracting and supporting the tissuesurfaces simultaneously. In the vertebral compression fractureapplication, it is preferable to distract along the Z-axis (along theaxis of the spine) to restore vertebral height. However, in otherapplications, it may be preferable to provide distraction in a differentdirection. The features of a wafer and a column of wafers will bedescribed relative to position and direction. The top of a wafer or thetop of the column is defined as the face of the wafer or column in thedirection of distraction. The bottom of a wafer or the bottom of thecolumn is defined as the face opposite the top face. In similar fashion,above and below a wafer or column implies along the top and bottom ofthe wafer or column, respectively. Each wafer has a leading edge thatenters the forming column first and a trailing edge opposite the leadingedge. The sides of the wafer are adjacent the leading and trailing edgesand the top and bottom faces of the wafer. In general, the sides arelonger than the leading and trailing edges, however the sides may beshorter than the leading and trailing edges. The axis of the column isdefined as a line parallel to the direction of distraction.

During implantation, the wafers are stacked to form a column tosimultaneously distract and support the two tissue surfaces. Theinvention provides that trailing wafers can be positioned above or belowthe leading wafers to form a column. In one embodiment, the wafers aredesigned to be beveled at both their leading and trailing edges so thatwhen lined up end-to-end, force on the trailing edge of the trailingwafer causes its leading edge to slide below the trailing edge of theleading wafer, thereby lifting up the leading wafer. Likewise, the bevelof the leading and trailing edges may be reversed enabling insertion ofa trailing wafer above a leading wafer. Alternately, the leading andtrailing edges may be chevron shaped or curved when viewed from theside, enabling insertion of trailing wafers between any two leadingwafers or on the top or bottom of the column. In another embodiment, thewafers may be configured with blunt edges wherein the wafers are stackedwith the insertion instrument. In all embodiments, by repeating theprocess with consecutive wafers, the column height increases to restorevertebral height.

The specific configuration of each wafer may be altered to better suitthe application for which the wafer will be used. For instance, thethickness of the wafer and the angle of the bevel may be varied toprovide a mechanical advantage and insertion force within acceptableranges for a given application. A more acute bevel angle will providegreater vertical force for a given insertion force. In addition, waferthickness may be varied to increase or decrease resolution available tothe physician in performing a given surgical procedure. A thinner waferwill provide greater displacement resolution and incremental forcegeneration to the physician in performing the procedure. A variation ofwafer thicknesses may be used in combination to form a column andmultiple wafers may be inserted into the column simultaneously. The topand bottom faces of a wafer may be parallel or oblique to enablebuilding a column that is straight or curved, respectively. Parallel oroblique-faced wafers may be used independently or in combination tobuild a column that has straight and/or curved sections.

In order to place the wafers between the tissue surfaces, a waferinserter is positioned within the surgical site with access at itsdistal tip to the tissue surfaces to be distracted and supported. Awafer is placed on the track and a plunger is used to advance the waferto the distal end of the track. This is repeated with consecutive wafersuntil a column of sufficient height is created per physician discretion.After the wafer(s) have been inserted, the insertion device is removed.The distal end of the insertion device may be manufactured from the samematerial as the wafers and/or be detachable. In this embodiment, thedistal end of the insertion instrument would be detached after placingthe wafer column, and the instrument removed.

Optionally, bone filler may be injected into the vertebra to furtherstabilize the distracted tissues. The first wafer inserted may be longerand/or wider than subsequent wafers. The size differential mayfacilitate bone filler flow around the wafers. In addition, the waferscan be designed with various tunnels, grooves, and/or holes to improvewafer encapsulation, bonding between the wafers and any injected bonefiller, and to provide a pathway for bone filler to penetrate the wafercolumn.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a vertebral body having a compression fracture displacingits superior and anterior edge.

FIG. 2 shows a vertebral body, following treatment of a compressionfracture.

FIG. 3 illustrates a plan view of a distraction device insertionapparatus according to an embodiment of the invention, placed within avertebral body shown in cross-section.

FIG. 4 illustrates a cross-sectional view of the insertion apparatus ofFIG. 3 deploying a distraction device according to an embodiment of thepresent invention.

FIG. 5 illustrates a cross-sectional view of the insertion apparatus ofFIG. 4 deploying a distraction device according to an alternateembodiment of the present invention.

FIG. 6 shows a plan view of a configuration of distraction deviceaccording to one embodiment of the present invention.

FIG. 7 shows an alternate plan view of the distraction deviceconfiguration of FIG. 6.

FIG. 8 shows a plan view of a configuration of distraction deviceaccording to an alternate embodiment of the present invention.

FIG. 9 shows an alternate plan view of the distraction deviceconfiguration of FIG. 8.

FIG. 10 shows a plan view of a configuration of distraction deviceaccording to an alternate embodiment of the present invention.

FIG. 11 shows an alternate plan view of the distraction deviceconfiguration of FIG. 10.

FIG. 12 shows a plan view of a configuration of distraction deviceaccording to an alternate embodiment of the present invention.

FIG. 13 shows a sectional view of the distraction device configurationof FIG. 12.

FIG. 14 shows a plan view of a configuration of distraction deviceaccording to an alternate embodiment of the present invention.

FIG. 15 shows a sectional view of the distraction device configurationof FIG. 14.

FIG. 16 shows a plan view of a configuration of distraction deviceaccording to an alternate embodiment of the present invention.

FIG. 17 shows an alternate plan view of the distraction deviceconfiguration of FIG. 16.

FIG. 18 shows a plan view of a configuration of distraction deviceaccording to an alternate embodiment of the present invention.

FIG. 19 shows an alternate plan view of the distraction deviceconfiguration of FIG. 18.

FIG. 20 shows a plan view of a configuration of distraction deviceaccording to an alternate embodiment of the present invention.

FIG. 21 shows an alternate plan view of the distraction deviceconfiguration of FIG. 20.

FIG. 22 shows a plan view of a configuration of distraction deviceaccording to an alternate embodiment of the present invention.

FIG. 23 shows an alternate plan view of the distraction deviceconfiguration of FIG. 10.

FIG. 24 shows a plan view of a distraction device according to analternate embodiment of the present invention.

FIG. 25 shows a plan view of a configuration of several of thedistraction device of FIG. 24.

FIG. 26 shows an alternate plan view of the configuration of thedistraction device of FIG. 25.

FIG. 27 shows a plan view of a configuration of distraction devicedeployed within a vertebral body, shown in sectional view.

FIG. 28 shows a plan view of a further configuration of distractiondevice being deployed within a vertebral body, shown in sectional view.

FIG. 29 show a sectional view of a portion of an insertion deviceaccording to one embodiment of the present invention.

FIG. 30 shows a sectional view of an entire insertion device, a sectionof which is depicted in FIG. 29.

FIG. 31 show a plan view of a series of undeployed distraction devicesconnected by a tether according to one embodiment of the presentinvention.

FIG. 32 shows a plan view of an alternate state of the distractiondevices of FIG. 31.

FIG. 33 shows a plan view of an alternate state of the distractiondevices of FIG. 31.

FIG. 34 shows a sectional view of an insertion device according to oneembodiment of the present invention.

FIG. 35 shows a sectional view of a portion of the insertion device ofFIG. 34.

FIG. 36 shows a sectional view of a portion of the insertion device ofFIG. 35.

FIG. 37 shows a sectional view of a portion of an insertion deviceaccording to an alternate embodiment of the present invention.

FIG. 38 shows a plan view of an alternate state of the insertion deviceof FIG. 37.

FIG. 39 shows a sectional view of an insertion device according to anembodiment of the present invention, configured to deploy distractiondevice similar to that depicted in FIGS. 31-33.

FIG. 40 shows a sectional view of an alternate state of the insertiondevice depicted in FIG. 39, configured for the removal of thedistraction device similar to that depicted in FIGS. 31-33.

FIGS. 41-45 show sectional views of an embodiment of an insertion deviceaccording to the present invention, with corresponding suitabledistraction device, in various states attendant to clinical deployment.

FIG. 46 shows a plan view of a clinical deployment device according toan alternate embodiment of the present invention, inserted into avertebral body, shown in cross-section.

FIG. 47 depicts the implementation of a regimen for treatment of avertebral compression according to an embodiment of the presentinvention, by plan view.

FIG. 48 depicts the implementation of a regimen for treatment of avertebral compression according to an alternate embodiment of thepresent invention.

FIG. 49 shows a plan view of an apparatus for use in deploying thedistraction device according to a further alternate embodiment of thepresent invention.

FIG. 50 shows a plan view of an apparatus for use in deploying thedistraction device to be used in conjunction with the apparatus of FIG.49.

FIG. 51 shows a plan view of an apparatus according to an embodiment ofthe present invention.

FIG. 52 shows an alternate plan view of the apparatus of FIG. 51.

FIG. 53 shows a plan view of the apparatus of FIG. 52 according to analternate state.

FIG. 54 shows a plan view of an apparatus according to an embodiment ofthe present invention.

FIG. 55 shows a plan view of an alternate embodiment of the apparatusdepicted in FIG. 54.

FIG. 56 shows a sectional view of an apparatus according to anembodiment of the present invention, suitable for deployment ofdistraction device similar to that depicted in FIGS. 31-33.

FIG. 57 shows a sectional view of an alternate configuration of theapparatus depicted in FIG. 56.

FIG. 58 shows a plan view of a bone filler insertion tool according toone embodiment of the present invention.

FIG. 59 shows a sectional view of the bone filler insertion tooldepicted in FIG. 58.

FIG. 60 depicts the implementation of a regimen for treatment of avertebral body according to an embodiment of the present invention.

FIG. 61 depicts the deployment of an insertion device according to anembodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The invention provides a combination of an implantable distractiondevice and instrumentation to place the device. The distraction deviceis detailed in this section by its application to the vertebralcompression fracture. FIG. 1 shows a vertebral body 60 having acompression fracture displacing its superior and anterior edge 62. FIG.2 shows a vertebral body 60 wherein the height has been restored.

The Distraction Device

A plurality of stackable wafers is provided for insertion between twotissues and is delivered to a surgical site along an axis transverse tothe axis of distraction. Multiple wafer insertions result in a column ofwafers at the surgical site that simultaneously distracts and supportsthe two tissues.

The wafers may be formed from a solid form of bone filler material,and/or any other suitable material such as but not limited toimplantable grade alloys (including, but not limited to titanium, cobaltchrome, nitinol, or stainless steel), other medical grade composites(including, but not limited to polyetheretherketone polymer (PEEK),ultra-high molecular weight polyethylene, or polyethylene) otherceramics (including, but not limited to zirconia, alumina, orcalcium-phosphate based ceramics), and resorbable polymers (for example,polylactic acid (PLA), polyglycolic acid (PGA), andpoly(lactide-co-glycolide) (PLGA)). The wafers may be dense or porous,while porous wafers may be filled with resorbable polymers to increasemechanical strength. For soft tissue applications, it may be desirableto manufacture the wafers of woven collagen pads, tissue engineeredmaterials, chitin, urethanes, silicone, or silicone materials.Alternately, the wafers may be manufactured from hydrogel (polyvinylalcohol) in which the wafer is inserted in a dehydrated form and expandswith fluids present at the insertion site. Hydrogel wafers may beparticularly desirable for placing in the disc space between vertebrae.For purposes of this disclosure, these materials and their combinationswill be collectively defined as the “implant materials.” Further, thewafers and implant materials may be combined with osteoinductive agents(including BMPs, growth factors, cell therapy, gene therapy, and patientderived factors) and other drug therapies. The osteoinductive agents maybe added to initiate and accelerate bone formation while the drugtherapies may range from antibiotics to reduce the risk of infection tochemotherapy to treat cancer. Optionally, the wafers may be used with aflowable bone filler material. For the purposes of this disclosure, bonefiller is defined as any substance used to stabilize the bone andincludes, but is not limited to bone cement (polymethyl methacrylatePMMA, or PMA), other composite material, human bone graft (allograft orautograft), synthetic and xenograft derived bone substitutes (calciumphosphate, hydroxylapatite, and/or other ceramic based bonesubstitutes), collagen, or combinations of these materials.

The invention provides that the wafer column is formed in vivo by usinga wafer inserter. FIG. 3 illustrates a wafer inserter 64 placed within avertebral body with a wafer 66 positioned distally on the wafer inserter64. During implantation, the wafers are stacked to form a column torestore vertebral height. FIGS. 25 and 26 show a wafer column 192supporting the proximal end plate of a vertebral body.

Consecutive wafer insertions result in a column of wafers at thesurgical site. In one embodiment, the trailing edge of a wafer isbeveled or otherwise configured to guide the next wafer under the first.FIG. 4 illustrates a wafer 70 being inserted under a preceding wafer 72.The leading edge 74 of the wafer is beveled to guide it under the onethe trailing edge 76 of the preceding wafer, which is correspondinglybeveled to guide the subsequent wafer underneath. Chevron and roundededges may be used in the same manner as beveled edges to guide theleading edge of one wafer under the trailing edge of another.Alternately, the wafer edges may be squared and the tool for insertingthe wafers may be used to lift the trailing end of the leading wafer andslide the trailing wafer thereunder as depicted in FIGS. 41-45.Similarly, any configuration of wafer or tool may be used to allow thewafers to stack into a column during insertion into the body.

The wafer design may be varied to suit the requirements of specificsurgical applications. Wafer thickness may range from 0.2 mm to 6 mm,and bevel angle (the angle between the leading and trailing faces of awafer and the direction of insertion) may range from 2 to 90 degrees.The mechanical advantage and the insertion force may be designed withinacceptable ranges for a given application by varying the thickness andthe bevel angle. A more acute bevel angle will provide greater verticalforce for a given insertion force. In addition, wafer thickness may bevaried to increase or decrease displacement resolution for a givensurgical procedure. A thinner wafer will provide greater displacementresolution and incremental force generation.

Specifically for vertebral compression fracture applications, exemplarywafer dimensions range as follows:

Wafer length between 5 mm and 40 mm;

Wafer width between 2 mm and 16 mm;

Wafer thickness between 0.2 mm and 6 mm; and

Curved wafer radii between 10 mm and 500 mm.

These dimensions are provided only as guidelines and any suitabledimensions may be used. Furthermore, the dimensions of the wafer willlikely vary widely when the wafers are used in other applications, suchas, for example, treating tibial plateau fractures.

The wafers may be rigid, as seen in FIG. 4, or may be flexible, as seenin FIG. 5. A rigid wafer may tend to pivot over the leading edge of thesubsequent wafer as it is inserted, placing a bending moment on thewafer. A flexible wafer 80 tends to conform to the leading edge of thesubsequent wafer as it is inserted. The stiffness of the wafer will bedependent on the material selected and the cross sectional geometry ofthe wafer. When stiffer materials are selected, the wafer thickness andbevel angle may be optimized to minimize the bending moment placed onthe preceding wafer or wafers.

In addition, the wafer thickness may be uniform or varied. Specifically,the wafers may be either flat or wedged, or alternatively include acombination of flat and wedged wafers. The wedge may increase inthickness from leading edge to trailing edge or vice versa, or mayincrease in thickness from side to side. The wedged wafers may be ofvarious angles. For example, the physician reducing a compressionfracture may observe that the column is not parallel to the end plate.As the end plate is returning to its anatomical position, anappropriately wedged wafer(s) may be inserted to gradually curve thecolumn to provide a parallel interface with the end plate. Similarly,the wafers may be wedge shaped with the anterior aspect of the waferthicker than the posterior aspect to reproduce the natural lordoticcurvature of the spine for interbody fusion. In addition, wafers ofdifferent thickness may be inserted into the same column.

A further option is to alter the interface of one wafer to a precedingor following wafer to suit a specific application. The interface mayprovide various degrees of freedom to accommodate various surgicalapplications. These include unconstrained, semi-constrained in selectdegrees of freedom, and totally constrained applications. Changing thewafer's surface configurations often varies the wafer interfaces. Thesurface configurations may be applied independently or in combination,based on the demands of the surgical application.

For example, if the wafers are to be implanted in a fashion that doesnot require alignment of one wafer to the next wafer, the interfacesbetween the wafers may be generally flat. This configuration provides asimple unconstrained wafer interface. The generally flat contact facesallow the wafers to translate relative to one another in the plane ofthe interface. They are also free to rotate about an axis normal to theinterfaces. Optionally, the wafers may be distracted from one another.

An unconstrained wafer configuration is shown in FIG. 6 where the wafers86 are flat wafers with no surface texture, that is, with surfaces thatmay rigidly slide on one another. These wafers are limited incompression along the Z-axis and rotation about the X- and Y-axes.However, distraction along the Z-axis is free. Translation and rotationare permitted along the X- and Y-axes in the plane of the interface.FIG. 7 provides an end view of the flat wafer 86 configuration.

On the other hand, if a semi-constrained wafer interface is desired, thewafers may be otherwise configured. For example, if the wafers aredesigned for placement in a vertical column wherein they are allowed toslide longitudinally, then the interfaces between the wafers may have alongitudinal groove 88 to align the wafers as shown in FIGS. 8 and 9.FIGS. 8-11 illustrate a preferred wafer embodiment. The wafers 90 havebeveled leading edges 92 and beveled trailing edges 94 to facilitatesliding of a subsequently inserted wafer under the leading wafer. Asseen in FIGS. 8 and 9, the wafers 92 include ridges 96 along theirbottom surfaces and corresponding grooves 98 along their top surfaces tolimit motion of one wafer to another. Similarly, the ridge may belocated along the top wafer surface and the groove located on the bottomsurface, as shown in FIGS. 10 and 11.

As shown in FIGS. 12-15, the wafer may have a “lip” built into theundersurface 100 and corresponding ridge 102 on the top surface of thesubsequent wafer to limit axial travel of the subsequent wafer along theX-axis or Y-axis as desired. The undersurface 100 is the surface of thewafer adjacent to the insertion track. The lip 104 can extend along theleading edge of the wafer (preventing translation along the X-axis) asseen in FIGS. 12 and 13, or the lip can extend along the lateral (notleading or trailing) edges of the wafer (preventing translation alongthe Y-axis), or as shown in FIGS. 14 and 15, the lip 106 can extendalong the lateral edges and the leading edge (preventing translationalong the X- and Y-axes). However, the lip should not extend along thetrailing edge of the wafer as such a configuration may interfere withthe interface between the wafer and the subsequent wafer. Furthermore,FIGS. 16 and 17 illustrate the lip in a tapered configuration 108 with amechanical detent 110 along the length of the taper. A correspondingtapered ridge 112 along top of the subsequent wafer engages the taperedlip 108. Similarly, the mechanical detents 114 on the tapered ridge 112engage the corresponding mechanical detents 110 in the tapered lip 108.The tapered lip may be configured without mechanical detents wherein thetaper angle would be such to promote a frictional lock between thewafers when axially loaded. Alternatively, the groove may be a dovetailto provide longitudinal sliding and a vertical lock between the wafers.

Another wafer embodiment, shown in FIGS. 18 and 19, involves wafers 120having cylindrical (arched surface) interfaces. The axis of the cylinderis along the X-axis of the wafer, allowing adjacent wafers to slidealong an arch about the X-axis. Such motion enables the top and thebottom of the column to conform to non-parallel tissue support surfaceswhile applying a distraction force to the tissue surfaces. The wafersare restricted in translation in the Y-axis and rotation about theZ-axis. If desired, the top 122 and bottom 124 wafers of a cylindricalcolumn may have flat top 126 and bottom 128 surfaces respectively, asseen in FIGS. 20 and 21, to facilitate uniform support by tissue supportstructures.

FIGS. 22 and 23 show an alternate wafer design providingsemi-constrained wafer interfaces 130. The wafers have spherical (or,optionally, hemi-spherical or less than hemi-spherical) interfaces thatprovide rotation about all three-principle axes. In this embodiment,translation along the X- and Y-axes and compression along the Z-axis arerestricted. Distraction along the Z-axis and rotation about the Z-, Y-,and X-axes are free. Optionally, the top and bottom wafers may be flat(not shown) on their top 132 and bottom 134 surfaces respectively. Ifflat, the top 132 and bottom 134 surfaces facilitate uniform supportfrom support structures.

In another embodiment, the semi-constrained wafer interfaces may bepinned to one another allowing rotation in the plane of the interfaceabout a fixed axis.

In yet another embodiment of semi-constrained wafer interface, the waferinterfaces may be keyed together to prevent distraction of the wafers.Such keyed interfaces may include but are not limited to a dovetail (seefor example FIG. 24), “T” bolt, or key hole design that allows thewafers to translate along the axis of the keyed elements. Translationnormal to the keyed elements, distraction, and rotation are restricted.

Another option is to constrain the wafer interfaces. In one suchembodiment, the wafer interface includes a combination of a keyedelement and a snap-in pin that can be used to allow sliding one waferonto another to provide lifting force. The keyed elements providerestriction of translation normal to the keyed element and distractionand rotation. The addition of a pinned element that snaps in placeprovides restriction of translation along the axis of the keyed element.

FIGS. 24-26 show a wafer configuration combining a dovetail 140 and acylindrical indent 142. This limits compression and distraction alongthe Z-axis, translation along the X- and Y-axes and rotation about theX-, Y-, and Z-axes. Thus, the wafers are constrained in all degrees offreedom.

Alternately, a constrained wafer interface may include a series (two ormore) of pressfit pinned interlocks that engage when one wafer isproperly positioned above another and the two wafers are compressedtogether.

If the wafers are intended for stacking in a vertical column withtranslation locked, the wafer interfaces may be keyed together with aboss on each wafer that fits into a mating cavity on an adjacent wafer.The boss may be of any suitable shape, such as cylindrical or square.Further, if vertical locking is needed, the boss feature may be combinedwith a dovetail or other keyed mechanism to lock the wafers fromvertical separation.

A further wafer option is to alter the shape of the wafers. The wafersmay be straight or may be curved along a constant radius extending froman axis parallel to the axis of the desired wafer column. In the case ofstraight wafers, stacking is longitudinal and the insertion instrumentdeploys the wafers linearly. In the case of curved wafers, stacking isalong the arch of the curve and the insertion instrument deploys thewafers along an arch. Reference is made to FIG. 46. Alternatively, thecurved wafers may have a ridge on the top surface of slightly differentconfiguration than that of the mating groove on the under surfacethereby creating a frictional lock when one wafer is inserted underanother. In all wafer embodiments containing mating ridges and grooves,the ridges are described as being on the top surface of the wafer andthe groove on the bottom surface. The wafers would function equivalentlyif the groove were on the top surface and the ridge on the bottomsurface.

In certain applications, it may be beneficial for the wafers to besecured to one another after insertion. Any suitable method for securingthe wafers to one another as known by those skilled in the arts may beused. Wafers may be secured to one another by means of an adhesive bond,a chemical bond, and/or a mechanical interlock (as described above).Applying a generic fluent adhesive, for example cyanoacrylate, into thecavity surrounding the column provides adhesive bonding. The fluentadhesive hardens and locks the wafers.

Introducing a liquid material that is chemically equivalent to the waferprovides a potential chemical bonding. For example, the wafers may bemanufactured from bone cement and bone cement may be injected around thewafers and into the vertebral body. The monomer in the bone cement mayinitiate a chemical bonding between the wafer and the bone filler,thereby locking the wafers together. A stable construct combined withcement interdigitation is believed to provide stability and pain reliefin a crushed vertebra.

It is also possible to enhance the wafer-to-wafer bonding and thewafer-to-bone filler bonding should bonding be desired. One method fordoing so involves solvent bonding in which the wafers are wiped with anappropriate solvent as they are inserted into the vertebra. A secondmethod involves coating the wafers with a microencapsulated solvent. Thesetting or hardening time for adhesives or solvent bonding may bedesigned to allow time to properly position the wafer column.Alternatively, the adhesives or solvents may be activated by additionalmeans such as light, heat, an activator, or other means that allowplacing and positioning the wafers before securing them to one another.

A preferred method of wiping the wafers with solvent includes equippingthe wafer inserter with a reservoir of solvent. A channel and wickdesign transports solvent to the distal end of the wafer inserter. Asthe wafers are inserted, they pass over the wick coating them withsolvent. Once inside the vertebra and formed as a column, the wafersbecome bonded to each other by solvent bonding. The solvent may alsoenhance the bonding of the wafers to the bone filler that may beinjected later in the procedure.

In order to coat the wafers with a layer of micro spheres containingsolvent, the wafers are coated prior to insertion. As the wafers arepassed through the wafer inserter and slide across one another in thecolumn, the micro spheres are ruptured to release the solvent. Thesolvent then bonds the wafers to one another and preps the outer surfaceto enhance bonding to the bone filler injected later.

The wafers may also include tunnels, grooves, or holes to facilitatemovement of bone filler through the wafer column into the surroundingbone. Further, openings may be provided through the wafers to allowcommunication between the tunnels, grooves, or holes or adjacent wafers.In any configuration, bone filler material injected into the wafercolumn would then flow through the column, fully encapsulating thewafers and better bonding the wafers to the bone filler.

A preferred wafer embodiment includes radiopacity to enablevisualization. For example, a radiopaque material such as a metal markeror barium sulfate may be combined with the wafer material when thewafers are manufactured. Injection molding of the wafers with an x-raymarker inside the wafer, machining the wafers with a pressfit hole foran x-ray marker, applying a layer of radiopaque epoxy, or bonding aradiopaque marker onto the surface of the wafer are other non-limitingexamples of inclusion of radiopaque materials. Alternatively, the firstand last wafers may be made of a suitable radiopaque material, such asmetallic or plastic, to enable visualization of the top and bottom ofthe forming wafer column under fluoroscopy.

In a clinical application, the wafers are inserted such that consecutivewafer insertions form a column. FIG. 27 illustrates a column 192 formedof equally sized wafers 194 inserted through wafer inserter track 196.However, in some situations it may be desirable to configure the top 198and bottom 200 wafers of the column 192 larger than the intermediatewafers 202 as shown in FIG. 28. The larger top and bottom wafers willprovide larger surface area over which to distribute loads. As thelarger, first wafer is elevated, a space is created between the edges ofthe subsequent wafers and the surrounding tissue. This space would beequivalent to the overhang of the first wafer. The final wafer, oralternatively, the detachable distal end of the inserter, may also belarger than intermediate wafers 108 so as to create an overhang similarto that of the first wafer while also increasing the contact area. Theend result is a channel around the interspaced wafers through which thebone filler may flow to fully encapsulate the wafers and tointerdigitate with surrounding tissue 204.

It may be advantageous to form multiple wafer columns extending axiallyin opposite directions. This can be done by a variety of differentmethods. One method involves using multiple wafer inserters. Forexample, if two opposing wafer columns are to be formed, then one waferinserter is deployed to form a wafer column directed superiorly, while asecond wafer inserter is deployed to form a wafer column inferiorly,opposite the first column. The separate wafer inserters may havedifferent access locations through the cortical wall of the vertebralbody. The wafer inserters may be parallel to one another, or skewed toone another, or one may enter the vertebral body through the ipsilateralcortex relative to the first wafer inserter. In addition, the waferinserters may be adjacent one another or may be separated by cancellousbone. Alternately, as seen in FIGS. 29 and 30, a single wafer inserter40 might be used wherein the wafer inserter is able to deploy wafers inopposing directions, one column deployed superiorly 212 and the otherdeployed inferiorly 214. Deployment of wafers in each direction may beindependent, in which case the physician, based on intraoperativeassessment, may expand the wafer column proximally or distally asneeded. Alternatively, wafer deployment may be simultaneous in eachdirection, in which case a wafer would be added to the wafer columnsforming in opposing directions.

The wafers may be connected, prior to implantation, by a tether. Thetether may be a thin ribbon manufactured of nitinol, suture, ribbon, orsimilar material. The tether may be thin and rope-like or wide andband-like. FIG. 31 shows an embodiment where the tether 218 runs alongthe top surface (224 of FIG. 32) of the wafer 220. The wafers 220 areplaced in the track 222 with the tether 218 connecting them. A side viewof the same embodiment is shown in FIG. 32. Connection via the tetherallows the wafers to be easily removed after placement. When a tether isused to connect the wafers, the wafers may also be formed with groovesor surface configurations to control translational movement.

Preferably, the wafers are molded around a tether wherein the tether ispositioned at the top of the wafers to form a continuous slidingsurface. The sliding surface prevents the wafers from “catching” on thewafer inserter as they are removed from the surgical site through thewafer inserter. The wafer is pulled up to the leading edge of the trackand the tether provides a smooth transition as the wafer is fed into thetrack during extraction. The length of the tether is slightly longerthan the length of a wafer to facilitate stacking the wafers in vivo.

The wafers connected via a tether are especially useful when the wafersare used as a bone tamp. This configuration may be used in situationswhere it is desirable to form a space between tissues and then removethe column. FIG. 33 shows an expanded column formed of wafers 220connected via a tether 218 to illustrate the path of the tether as thecolumn is formed. An implant manufactured from any of the materialspreviously described may be placed in the cavity created by the removedcolumn of wafers, or bone filler may simply be injected.

Further embodiments of the connected wafer configuration include usingtwo tethers running along the lateral edges of the top surface of thewafers. The wafers and tether may alternately be integrally formed as acontinuous string of wafers. In this embodiment, the string of wafers isconfigured from a continuous piece of material wherein the wafers andtether are integrally formed. The tether enables stacking of the wafers.Yet another embodiment involves placing a wire mesh formed of smalldiameter wire, for example 0.001″, along the top surface of the wafers.The wire is optionally stainless steel, nitinol, or other suitable metalor plastic or fabric. Furthermore, the wafers may be spaced and securedinside a woven tube to enable stacking of the wafers once inserted bythe wafer inserter. The wire tube is woven of a wire mesh formed of asmall diameter wire, for example 0.001″ diameter. The tube has acircumference equal to the cross-sectional circumference of a wafer.

The Wafer Inserter

A wafer inserter is provided as part of the invention to deliver thewafers to the surgical site and to form a column of wafers. In oneembodiment, the wafer inserter applies a force along the X-axis (theaxis of insertion) to a wafer that is to be added to the column. Aspreviously described, the wafers may be configured with beveled ends tofacilitate lengthening along the Z-axis of the column as the additionalwafer is inserted. In an alternate wafer embodiment also previouslydescribed, the edges of the wafers are squared and the wafer inserterraises the leading wafer to place the trailing wafer thereunder.

Numerous variations of the wafer inserter are possible, the embodimentsgenerally including, but not limited to, a track, a plunger, and acartridge. The wafer inserter is comprised of a track, which is a longnarrow channel through which wafers pass when placed into the wafercolumn. A plunger generally advances wafers down the track. Multiplewafers are housed in a cartridge of the wafer inserter for advancementdown the track. Preferably included is a mechanism for feedingsubsequent wafers into the track in front of the plunger. Further, thetrack is configured for removal from the surgical site while leaving thewafer column intact.

In a hand-held embodiment, a mechanical mechanism is provided forconverting grip strength into a force to advance the plunger. The waferinserter may include a device to measure the force applied to theplunger or along the axis of the wafer column. This device may be, forexample, a force transducer. A device, for example a counter, may alsobe included to monitor the number of wafers inserted. The total forceapplied may be thus monitored and may reference a preset adjustableforce guideline. A device to display the measured force and/or thenumber of wafers inserted may also be included. It may be desirable toprovide a mechanism to limit the force applied along the axis of thewafer column as well as means for the physician to adjust such force.Additionally, in order to inject bone filler to further stabilize thewafer column, a means to open the channel of the track to accommodatesuch bone filler may be provided.

One embodiment of the wafer inserter is illustrated in FIG. 34. Thehandle 230 may be gripped to position the wafer inserter 232. The waferinserter 232 has, at its proximal end 234, a magazine 236 containingwafers 238. The wafers 238 may be stacked in the magazine 236 with a topsurface of one wafer supporting the bottom surface of an adjacent wafer.The handle 230 is equipped with a trigger 240 for forcing wafers out ofthe magazine 236. Optionally, the magazine 236 is equipped with a spring242 to load wafers 238 along the track 244 of the inserter 232. Thetrack 244 of the inserter 232 extends from the magazine 236 to thesurgical site at its distal end 246. As they enter the wafer track 244,the wafers 238 are aligned with the leading edge of one wafer adjacentthe trailing edge of a preceding wafer. The track 244 in the embodimentshown in FIG. 34 includes a lower cavity 250 and an upper cavity 252.The plunger extends through the lower cavity 250 while the wafers 238are aligned along the upper surface of the plunger. An opening isprovided along the top surface of the lower cavity 250 at the distal end246 of the track 244 to accommodate a wafer. Thus, as the plunger isretracted past the trailing edge of the furthest distal wafer, the waferdrops into the lower cavity. The plunger pushes the wafer distally toform a column of wafers 254. FIG. 35 provides a close up of the waferinserter magazine 236, track 244, and distal end 246. FIG. 36 shows anextreme close up of the distal end 246 of the wafer inserter 232 alongthe track 244.

A wafer inserter configured for deployed wafer columns in oppositedirections is depicted in FIG. 30. Two triggers, 211 and 213 areincluded in the handle 230 and are operatively coupled to upper andlower magazines of wafers 210 and 209, respectively. The upper trigger211 inserts a wafer at the bottom of the top wafer column 212 andadvances that column superiorly (in the positive Z-axis). The bottomtrigger 213 inserts a wafer at the top of the lower wafer column andadvances that column inferiorly (in the negative Z-axis). Alternatively,the wafer inserter could be designed so that one trigger could controlboth columns independently. Other configurations for deploying opposingwafer columns with a single wafer inserter may be used as would beobvious to a person skilled in the art.

Another possible wafer inserter embodiment includes a modular design,including a cartridge and track detachable from the handpiece. All thecomponents may be disposable, or alternatively reusable, or somecombination thereof. Such a design may simplify the use of multiplewafer sizes and configurations.

One method to deliver the wafers is through an inserter that guides thewafers into position and provides the force along the X-axis to slideone wafer under another and provide the lifting force across the heightof the column to meet the surgical demands of the procedure. Theinserter may be a fixed tip inserter but may also be a detachable tipinserter.

The fixed tip inserter provides a floor over which the wafers slide intoposition. The fixed tip references the distal tip of the wafer insertertrack that directly supports the wafer column. A catch is designed atthe distal end of the floor to hold the first wafer in place while thesecond wafer is inserted under the first. The second wafer elevates thefirst wafer and begins the wafer column. The second wafer is then heldin place by the distal catch while the third wafer is inserted. Theprocess is repeated until the desired column height is attained. Thedistal catch may engage the bottom wafer only or, optionally, may beconfigured to engage the bottom two or more wafers. If the slidingfriction between the wafers results in an axial force that would advancethe upper wafer while the lower wafer is inserted, having the catchengage the second wafer would prevent displacement of the upper waferwhile building the column. However, if the friction is lower than theforce to advance the upper wafer (i.e. the strength of the surroundingcancellous bone or tissue), then a shorter catch to engage only thebottom wafer would be adequate.

In the fixed-floor embodiment of the wafer inserter, wafers are inserteduntil the required height or force is attained. At that point, thedistal catch is released. A longer plunger (removal plunger) may be usedto remove the inserter. The removal plunger is placed along the track ofthe inserter and the inserter advance mechanism is used to push theinserter out of the vertebral body. The removal plunger pushes againstthe bottom wafer. The bottom wafer retains its position in the columnwithin the vertebra and the reaction force forces the wafer inserter outfrom the vertebra. Similarly, the standard plunger may be designed withselectable travel. The plunger may be set to insert wafers, or toadvance further and remove the wafer inserter. The height of the wafercolumn would be reduced by the thickness of the fixed tip, whichpreferably would be approximately 0.010″ to 0.020″ thick.

The detachable tip wafer inserter embodiment, as seen in FIG. 37,includes a distal tip 260 of the wafer inserter 262 that is detachablefrom the main portion 264 of the inserter. One advantage provided by thedetachable tip is that the height of the wafer column is not alteredwhen the wafer inserter is removed. The tip 260 is preferablymanufactured of the same material as the wafers. Thus, in a preferredembodiment, if the wafers are manufactured of PMMA, the distal tip 260of the wafer inserter 262 is manufactured of PMMA. Alternately, thedistal tip 260 may be manufactured of an implant grade metal or othermedical grade implantable material. The distal tip 260 has a fixeddistal shoulder 266 that holds the first wafer in place while the secondwafer is inserted under the first. The height of the distal shoulder 266may provide a stop for one wafer, or it may provide a stop for two ormore wafers. The considerations applicable to the height of the distalcatch apply to the height of the distal shoulder as well.

In the detachable tip embodiment, wafers are inserted until the desiredheight or force is attained. As seen in FIG. 38, the distal tip 260 isthen released from the main portion 264 of the wafer inserter and themain portion 264 of the inserter is removed. The distal tip may bepress-fit onto the track or may be bonded with an appropriate adhesive.In either case, the interface is designed to support the forcesgenerated while building a wafer column, but shear when the extractionplunger is used to remove the wafer inserter. Optionally, the distal tip260 may be keyed to interlock with the main portion 264 of the waferinserter. For example, the main portion of the inserter may interlockwith the distal tip by spring-loaded hooks that are mechanicallycompressed when the tip is to be released. Alternately, the hooks may bespring-loaded in the release position and mechanically expanded toengage the distal tip. In another embodiment, the detachable tip may bepress-fit onto the wafer inserter or bonded with a weak adhesive. Whenthe wafer inserter is to be removed, a force may be applied using alonger plunger or equivalent mechanism as in the fixed tip waferinserter to dislodge the removable tip. The track of the wafer insertermay be then removed.

Both the fixed tip and detachable tip wafer inserters can be configuredto deploy wafers in opposing columns. In such an embodiment, one columnmay be built in the positive Z-axis. Thus, if the supporting bone belowthe distal end of the track begins to yield, a second column in thenegative Z-axis can be built by inserting wafers below the track. Oncethe negative Z-axis column has provided enough support for the waferinserter, insertion of wafers into the positive Z-axis column can beresumed. The considerations applicable to distal stop or catch andmaterial selection previously described also apply to the bi-directionalwafer inserter. Reference is made to FIG. 30.

When inserting wafers connected via a tether, it is preferred to use thewafer inserter embodiment shown in FIG. 34 but the inserter may beeither fixed tip or detachable tip. (A cross-sectional view of the trackused to deploy tethered wafer is provided in FIG. 57). The wafers arestacked in a cartridge in the wafer inserter. To position the wafers,the wafers are advanced along the top of the plunger and the end mostwafer is inserted at the bottom of the column. FIG. 39 shows the wafers270 in the wafer inserter 272 being inserted into the surgical site. Inorder to remove the column 274, the bottom most wafer is removed first.In FIG. 40, the entry port at the distal tip 276 of the wafer inserter272 provides a fulcrum over which the tether slides. This ensures thatsubsequent wafers are pulled down, then out of the wafer inserter trackwithout twisting relative to the track.

A number of options relating to both the wafer inserter and the wafersare available. FIGS. 41-45 show wafers 280 having squared ends 282 beinginserted with a wafer inserter that lifts the leading wafer. When thetrack 284 of the wafer inserter is placed in the prepared channel in thesurgical site, the wafer elevator 286 is in its down position, as seenin FIG. 41. A force (F1) is applied to the wafers in the deliverychannel of the wafer inserter. FIG. 42 shows the first wafer 288advancing past the wafer elevator 286. The wafer elevator 286 flexes toallow the wafer 288 to pass into the lifting section of the waferinserter. The wafer 288 then proceeds to the distal stop 290 of thewafer inserter track 288, as seen in FIG. 43. The wafer elevator 286 isdrawn back slightly to clear the inserted wafer 288. As seen in FIG. 44,the elevator 286 is then advanced (F2) to engage the bottom surface 292of the newly inserted wafer 288. A force (F3) is applied to the waferinserter to advance another wafer 294 under the inserted wafer 288. Asthe wafer 294 is inserted it pushes the wafer elevator 286 to engage thewafer 288 or column of wafers previous inserted and elevates theproximal end 296 of the lower most wafer 288. The new wafer 294 is theninserted at the bottom of the column. FIG. 45 shows this processrepeated with consecutive wafers to create a column as may be desired.

As seen in FIG. 46, an alternate embodiment of the wafer inserterinvolves a wafer inserter 300 designed for inserting curved wafers 302.There may be surgical or structural advantages to inserting wafers thatare curved in a transverse plane. FIG. 46 also illustrates how a curvedwafer 302 may better fit the anatomy of the vertebral body.

Curved wafers may be inserted using either embodiment of the previouslydescribed wafer inserters (fixed tip or detachable tip) by incorporatinga curved wafer track. The wafer and track are then configured to have aconstant radius. The instruments to prepare the vertebra for theinserter are similar to the ones described for the straight inserter,but designed to function along a curve. The curve is set toapproximately match the anterior curvature of the vertebral body and maybe provided in a range of radii to accommodate patient size variationand variation in vertebral shape along the length of the spine.Alternatively, the curved wafer inserter can be configured to deploywafers in opposing columns. The bi-directional deployment of wafers maybe independent, enabling the physician to increase either column asneeded, or wafer deployment may be linked, in which case a wafer wouldbe inserted into each column simultaneously.

Distraction Device and Procedure Applied to Vertebral CompressionFractures

The ability to enter the vertebral body via an extrapedicular approachdramatically increases the cross sectional size available for placing adevice into the vertebral body. Current extrapedicular surgicaltechniques use a 6 mm ID cannula. According to the present invention, arectangular cannula of approximately 4 mm to 12 mm in width in atransverse plane and approximately 6 mm in height in a vertical planecan be placed into the lumbar and lower thoracic spine. Upper thoracicvertebrae, however, may be limited to a width of 3 mm to 8 mm in atransverse plane and a height of 3 mm to 6 mm in a vertical plane.

FIG. 47 illustrates an extrapedicular approach to a vertebral bodywherein an access channel 304 is placed through the posterolateral wallof the vertebral body. Other approaches may optionally be used forplacing the wafer inserter or inserters, although this may limit theaccess channel dimensions and corresponding implant size. FIG. 48illustrates a transpedicular approach to the vertebral body wherein anaccess cannula 306 is placed through the pedicle. In the extrapedicularapproach, cannulae may be placed bilaterally, through each pedicle.Similarly, two cannulae may be placed bilaterally using theextrapedicular approach, one on each side.

A preferred procedure for placing the wafers involves placing a guidewire into the vertebral body via an extrapedicular approach underfluoroscopy. An example guide wire 310 is illustrated in FIG. 49. Acannulated tamp is placed over the guide wire and advanced to thevertebral cortical wall. In one embodiment, as seen in FIG. 50, the tamp312 is cylindrical and is shown with a detachable handle 314. One methodof advancing the tamp into the vertebra involves tapping the tamp with ahammer or pushing/twisting the tamp by hand. Preferably, tampadvancement is monitored with a fluoroscope to place the distal tip ofthe tamp past the midline and spanning the midsection or anterior aspectof the vertebral body. Ideally, the tamp references or is indexed to theguide wire to minimize advancement of the tamp beyond the length of theguide wire. After advancing the tamp through the vertebral body to itsdesired position, the tamp is removed and the guide wire is left inplace.

An expandable access channel is advanced over the guide wire into thevertebra through the opening created in the vertebral body. Again, thechannel may reference the guide wire to prevent advancing the channelbeyond the length of the guide wire. Expanding the channel permitsadjustment of the channel to a size sufficient for receiving a waferinserter. FIG. 51 shows one embodiment of the expandable access channel316 where two channels 318 and 320 are placed together with their opensurfaces facing one another. FIG. 52 shows the two channels 318 and 320in a “closed” configuration, while FIG. 53 shows the two channels 318and 320 in an open configuration. The closed expanding channel 316 isplaced over the guide wire 310 and advanced into the vertebral body tothe tip of the guide wire. The guide wire is removed. Position of theexpanding channel and subsequent tapered and blunt expanders should bemonitored via fluoroscope. While an expandable access channel isspecifically discussed and contemplated, it is possible to use an accesschannel or series of channels which is not expandable and which is atits fullest dimension before advancement into the vertebra.

Once the expandable access channel is in place, the guide wire may beremoved. With the expandable access channel in place, a mandrel isplaced inside the channel. The mandrel should be larger than thecollapsed channel in order to expand the channel as the mandrel isdriven distally. As seen in FIG. 54, the mandrel 322 may have a taperedend 324 for ease of deployment. Optionally, the mandrel may have a shapecorresponding with the shape of the access channel. Thus, when arectangular access channel is employed, a rectangular mandrel may beused. Advancing the mandrel through the length of the access channelexpands the open channels in a transverse plane creating a cavity in thevertebral body corresponding in shape to the shape of the expandedaccess channel. It is preferred that a second mandrel is provided with ablunt end in the event that the tapered end of the first mandrel doesnot fully expand the access channel. FIG. 55 depicts a blunt-end mandrel326. In either case, the mandrel should reference the access channel toprevent advancement of the mandrel beyond the length of the channel.Optionally, a series of sequentially larger mandrels may be used togradually enlarge the expanding channel. A hydraulic expansion device,or other suitable expansion device obvious to those skilled in the art,may alternately be used to enlarge the expanding channel.

In a first embodiment of the invention, the mandrel is removed from theexpanded access channel and a wafer inserter is passed through thechannel. The wafer inserter may be a track, preferably having a lip atits distal end for preventing the wafers from sliding too far into thevertebra, and is inserted within the access channel. The distal end ofthe wafer inserter placed in the surgical site may be set by a positivestop at the proximal or distal end of the expandable access channel, orvisually using fluoroscope. FIG. 3 illustrates a wafer inserter track 64in position in the vertebral body.

It is recommended to keep the access channel in position during theentire procedure. This will ensure minimal invasiveness of theprocedure. Removal of the access channel risks inability to locate thechannel already created.

The wafer inserter includes a plunger that slides within a track foradvancing wafers down the track into the vertebral body. To position awafer in the vertebral body, a wafer is placed in the track and theplunger is advanced to full forward position to place the wafer at thedistal end of the track. To place a second wafer on the track, theplunger is retracted to the point where a second wafer drops from thecartridge of wafers to a position in front of the plunger. The plungeradvances the wafer to slide the second wafer underneath the first wafer.The force applied to the trailing edge of the second wafer causes thefirst wafer to be raised.

Various configurations of the wafer inserter and access channel areprovided. As seen in FIG. 56, the wafer inserter track 330 passesthrough the expanded access channel 332. The track 330 is sized topermit only one wafer to pass there through. The plunger 334 is sized tofill the wafer inserter track's internal opening. Alternatively, theexpandable access channel 332 may be interchanged with a non-expandableor fixed dimension access channel.

FIG. 57, shows a wafer inserter and access channel configuration whereinthe wafer inserter track 330 is sized for accommodating the plunger 334with a wafer 336 resting on top of the plunger 334. The wafers 336 arefed through the wafer track 330 on top of the plunger 334. When theplunger 334 is retracted the length of one wafer, a wafer drops down infront of the plunger. When the plunger is advanced, the wafer is theninserted under the column of wafers. Simultaneously, a wafer from thebottom of the column in the cartridge is advanced along the top of theplunger.

FIG. 37 shows a column 261 of wafers 263 being formed using a detachabletip wafer inserter 262, the tip 260 of which is detachable from the bulkof the wafer inserter 264. The process of inserting wafers is repeatedwith consecutive wafers until a column of sufficient height is createdto restore the vertebral body height per physician discretion. Duringrepetitions, vertebral body height and wafer position should beperiodically checked via fluoroscope.

Alternately, a plurality of pre-stacked wafers may be inserted at onceas a stack. Multiple wafers may be inserted simultaneously to vary thethickness added to the column in a single step, each stack of wafersthus acting as a single wafer insertable unit. Multiple wafers added maybe of the same thickness or varying thicknesses. In this case, the waferinserter would provide an option to select one, two, three or morewafers to be inserted simultaneously. Once selected, the wafer inserterfeeds the stack of an appropriate number of wafers into the track andthe stack is advanced into the wafer column. The wafer inserter elevatesthe preceding wafer to facilitate insertion of multiple wafers. Waferstacks of any suitable size may be mixed to form a column in vivo.

If desired, the wafer inserter may be positioned intermediate to twoinserted wafers. That is, the wafer inserter may be positioned along thewafer column. Thus, a subsequently deployed wafer would be insertedintermediate to previously inserted wafers. In this embodiment, thewafer inserter may be configured for insertion of the wafer in avertical down direction, a vertical up direction, or any directionsuitable for forming a column with the previously inserted wafers.

In the example of vertebral compression fracture reduction, thecancellous bone below the wafer inserter may not provide adequatesupport for the wafer column when reducing the proximal end plate. Insuch situations, it may be advantageous to deploy wafers proximally atthe start while monitoring distal displacement of the wafer inserter. Ifthe wafer inserter displaces distally, then wafers may be inserteddistally to maintain the initial position of the wafer inserter.

Although the wafers may be straight or curved, straight wafers wouldlikely provide the greatest surgical simplicity. Additionally, straightwafers more closely mimic current surgical techniques. However, a curvedwafer requires a similar and only slightly modified technique ofpercutaneously placing a curved delivery instrument. The curved waferoffers an improved anatomic match between the wafer column and theanterior cortex of the vertebra, thereby increasing the surface area andavailable distraction force. Compression fractures typically involvecollapse of the superior end plate in a generally flat fashion rotatingabout a coronal axis at the superior aspect of the posterior vertebralwall.

A curved wafer inserter may enable placement of the wafer more anteriorin the vertebral body while increasing the implant surface area andassociated distraction force. In vertebral compression fractures, thesuperior end plate is often displaced distally at an oblique angle abouta coronal axis at the intersection of the superior end plate and theposterior wall of the vertebral body. This results in compaction of theanterior cortical wall and the underlying cancellous bone. Placingcontoured wafers anteriorly to provide interior distraction that reducesthe superior end plate would be advantageous; the wafer column would bepositioned in a high weight bearing area of the vertebra.

When the fracture is reduced, or when the physician determines that anadequate number of wafers have been inserted, the wafer inserter may beremoved with a removal plunger. The expanding access channel is left inplace. Alternatively, if the distal tip of the wafer inserter isdetachable, then upon removal of the wafer inserter, the tip is detachedand remains inserted in the vertebral body as part of the column. Again,the expanding access channel is left in place.

After an adequate column of wafers is inserted, bone filler may beinjected into the vertebra to encapsulate the wafers, provide weightbearing structure, and increase stability. The bone filler bonds thewafers to one another as well as to the filler mantle thatinterdigitates with the cancellous bone. The wafers may be solid inconstruction and thus require the filler to flow around the wafer columnand bond to the outer surfaces of the wafers. Wafer-to-wafer bonding isthen achieved through solvent activation of wafer interfaces viacapillary effect. Alternately, the wafers may include tunnels totransport bone filler through the wafer column and out to thesurrounding bone. Bone filler material would be injected into the wafercolumn and then flow through the column.

If bone filler is injected, an injection channel (340 of FIG. 58), whichmay prefilled with bone filler, is advanced along the channel into thevertebra. The bone filler should be allowed to thicken to the desiredconsistency before injection into the vertebral space. The injection ispreferably completed under fluoroscopic observation to monitor bonefiller flow. The total amount of filler injected is subject to physicianjudgment. The physician may elect to use additional injectionchannel(s).

If the introduction of bone filler is desirable, the injection channelmay be passed through the expandable access channel. The injectionchannel is advanced until it approximates the wafer column. Theinjection channel includes a channel through which the bone fillerflows, and a plunger to eject bone filler. FIG. 59 provides across-sectional view of the bone filler injection channel 340. The tipof the plunger 342 is of slightly larger cross-sectional area than theplunger 344. Thus, the plunger 344 is slightly smaller than the channel340 and is easily inserted there through. The tip 342 is large enough toensure complete coverage of the bone filler.

Once in position, the plunger on the bone filler delivery channel isadvanced to inject the bone filling into and around the wafer column andthe surrounding cancellous bone. In the event that bone filler from onedelivery channel does not fill the vertebral body as per physician'sdiscretion, then additional delivery channels can be filled with bonefiller and bone filler delivered to the vertebral body in like fashion.Alternatively, any commercially available bone filler system may beused. Throughout the injection of bone filler, the vertebral bodyfilling should be monitored under fluoroscopic guidance in order toavoid extravasation.

Typically, the physician will have more control over cement delivery andflow when the cement is delivered under low pressure. Delivering cementthrough larger cannula, either circular or rectangular in cross-section,will promote more uniform (laminar) flow at larger delivery pressures.The current preference is to deliver cement through a cylindrical tube.The present invention enables use of a channel with a significantlylarger cross-sectional area. For example, the cross-sectional area of a6 mm ID tube is 28 mm². A rectangular tube would enable up to a 6 mmvertical height and up to 12 mm in a transverse plane for across-sectional area of 82 mm². This provides a more than 150% increasein cross-sectional area.

The injection channel is left in place until the bone filler hasthickened sufficiently that it will not flow out of the injection holeupon removal of the injection channel. The injection channel and theaccess channel are removed. Alternatively, the wafer inserter may remainin place and the bone filler may be injected through that device or thebone filler may be injected through any commercially available bonefiller delivery system.

FIGS. 27 and 28 show two wafer column embodiments with cementinterdigitation and with cancellous bone around the wafer columns. Asseen in FIG. 28, the top and bottom wafers 198 and 200 respectively maybe configured larger than the intermediate wafers 202 of the wafercolumn 192. This facilitates full encapsulation of the wafers by thebone filler. Bone cement fills the space left around the wafer column192. Alternatively, as seen in FIG. 27, the wafers 194 of the wafercolumn 192 may be of constant size with bone cement filling the spacesurrounding the wafer column 192.

Another embodiment involves a wafer column built within a permeablemembrane, the membrane having macro porosity. The membrane allows bonefiller to flow through its wall into surrounding cancellous bone toprovide better flow control, bone/filler interdigitation, stability, andstructural support. Flow can thereby be controlled into surroundingcancellous bone as well as on and into the wafer column.

The Distraction Device Applied to Tibial Plateau Compression Fractures

The current invention also provides an instrument that can place wafersin a vertical column to reduce tibial plateau compression fracturesthrough a minimally invasive approach. Thus, the implant simultaneouslyreduces the fracture and stabilizes the fracture.

In treating isolated compression fractures of one or both tibialcondyles, a pathway to the underside of the depression is achieved byplacing a guide wire percutaneously to a position that traverses theunderside of the depression. The instrumentation for placing the implantis placed as described above in reference to vertebral compression. Thatis, a cylindrical tamp is advanced over the guide wire and then removedto allow an expandable channel to be placed and a wafer inserterpositioned therein. Alternatively, a fixed dimension access channel maybe used in place of the expandable channel.

Once in position, the wafer inserter places wafers in a vertical columnunder the compression fracture. The wafers are inserted until thearticular surface is reduced (as confirmed by fluoroscopic orarthroscopic assessment). In treating an isolated tibial plateaucompression fracture, the wafers may be used alone, or with aninjectable bone filler material. The pathway through the tibial lateralwall may be filled with bone filler, or alternatively left to heal bynatural bone. In cases where both a compression fracture and a splittingfracture are present, the splitting fracture may be reduced andstabilized by minimally invasive placement of one or more bone screws.After stabilizing the splitting fracture, the compression fracture canbe reduced and stabilized as described for the isolated compressionfracture.

Alternatively, removable wafers may be inserted under the compressionfracture to reduce the fracture. Once reduced, the wafers are removedand the cavity created is filled with suitable bone filler material, orwith wafers fabricated from allograft bone or other suitable bonesubstitute materials.

The Distraction Device Applied to Spinal Interbody Fusion

In performing spinal interbody fusion, the wafer inserter is placedthrough the annular wall from a posterior approach, or aposterior-lateral approach. At least four procedures are contemplatedfor performing spinal interbody fusion with the wafer device. Theseinclude a posterior approach, a posterior lateral approach, an anteriorapproach, and an extrapedicular approach.

Surgical Procedure—Posterior Approach

The posterior approach, as shown in FIG. 60, involves two columns ofwafers each inserted lateral to a mid-sagittal plane. This is preferablydone using two wafer inserters 350 and 352 allowing gradual distractionof the annulus in a parallel fashion. The wafer inserters may beequipped with load sensors to provide a digital readout of the loadbeing applied by each column of wafers. This enables improved balancingof the distraction forces on each side of the annulus.

Surgical exposure is made to the posterior of the spine to access theposterior aspect of the annulus. Preferably, two openings are preparedin the annulus, each lateral to the mid-sagittal plane. The openings maybe a straight-line incision, or a “C” shaped incision extending to thenucleus. The nucleus is then removed.

Bone spreaders/shavers are placed in the two openings and the vertebralbodies are distracted. The bone shaver or similar device is operated toremove the central portion of the annulus. A generally flat surface downto the bleeding bone of the superior and inferior endplates is prepared.The end plates are decorticated down to bleeding bone.

The prepared surface supports the wafer columns. A wafer inserter isplaced in each opening and used in the manner described above. It ispreferred to insert wafers in an alternating fashion between the twoinserters to uniformly distract the annulus.

Annular tension is monitored as an indication of stability. Whenadequate stability is achieved as per physician discretion, no furtherwafers are inserted and the wafer inserters are removed. After removal,the incisions may be closed using standard techniques.

Surgical Procedure—Posterior-Lateral Approach

In the case of a posterior-lateral approach, one wafer inserter may beused with a wafer sized to cover the prepared endplates of opposingvertebral bodies.

A guide wire is percutaneously placed through the posterior-lateralsurface of the annulus into the nucleus. An opening is prepared in theannulus by advancing a cylindrical cutter over the guide wire. An accesschannel is placed over the cutter and advanced to the annulus.Preferably, the access channel is then locked to the annulus and theguide wire and cutter are removed. The nucleus may then be extracted.

A bone spreader/shaver is placed through the access channel to distractthe vertebral bodies. As in the posterior approach, the bone shaver orsimilar device is operated to remove the central portion of the annulus.A generally flat surface down to the bleeding bone of the superior andinferior endplates is prepared. The end plates are decorticated down tobleeding bone.

The prepared surface supports the wafer column. A wafer inserter isplaced through the access channel and used in the manner described aboveto insert wafers and distract the adjacent vertebral bodies.

Annular tension is monitored as an indication of stability. Whenadequate stability is achieved as per physician discretion, no furtherwafers are inserted and the wafer inserters are removed. After removal,the incisions may be closed using standard techniques.

Surgical Procedure—Extra pedicular Approach

A guide wire is percutaneously placed through the posterior-lateral wallof an adjacent vertebral body. The guide wire should be angled in afashion to enter the nucleus. A cylindrical tamp is advanced to enlargethe opening. After the opening has been enlarged, an expanding accesschannel is placed over the tamp and advanced to the vertebral body. Theaccess channel is locked to the vertebra and the guide wire and tamp areremoved. The expanding access channel is enlarged to enable placement ofa bone shaver and the wafer inserter. The nucleus may then be extracted.

As in the posterior-lateral approach, a bone spreader/shaver is placedthrough the access channel to distract the vertebral bodies. The boneshaver or similar device is operated to remove the disc's annulus. Agenerally flat surface down to the bleeding bone of the superior andinferior endplates is prepared. The end plates are decorticated down tobleeding bone.

The prepared surface supports the wafer column. A wafer inserter isplaced through the access channel and used in the manner described aboveto insert wafers and distract the adjacent vertebral bodies. FIG. 61illustrates a wafer inserter 64 in position in a vertebral disc.

Annular tension is monitored as an indication of stability. Whenadequate stability is achieved as per physician discretion, no furtherwafers are inserted and the wafer inserters are removed. After removal,the incisions may be closed using standard techniques.

While a preferred embodiment of the present invention has beendescribed, it should be understood that various changes, adaptation andmodification may be made therein without departing from the spirit ofthe invention and the scope of the appended claims.

What is claimed is:
 1. A curved expandable interbody fusion device forimplantation into the intradiscal space between opposing vertebralbodies in a spine, comprising: a curved elongate upper element includingan outer surface for engaging a first vertebral body, a lower surfacegenerally opposite said outer surface, a leading end and a trailing end,said curved elongate upper element being curved in a first plane; acurved elongate lower element including an outer surface for engaging anopposing vertebral body, a leading end and a trailing end, said curvedelongate lower element being curved in a second plane, said first planeand said second plane being generally parallel to each other, said upperelement being movable in an expansion direction away from said lowerelement; an elongate expansion member between said upper element andsaid lower element and movable along a path in a first direction that issubstantially perpendicular to said expansion direction, said expansionmember including a beveled lifting surface operable upon movement ofsaid expansion member to engage the lower surface of said upper elementto move said upper element away from said lower element in the expansiondirection and expand said device, said first plane and said second planebeing generally parallel to said first direction.
 2. The device of claim1, wherein said elongate expansion member has a leading end and atrailing end, said elongate expansion member being curved in a thirdplane between said leading end and said trailing end, said third planebeing generally parallel to said first and second planes.
 3. The deviceof claim 2, further comprising a cooperating constraint engageable uponslidable receipt of said expansion member between said upper element andsaid lower element to constrain relative movement between said upperelement and said expansion member in a direction transverse to saidfirst axial direction.
 4. The device of claim 3, wherein saidcooperating constraint comprises one of an elongate ridge or elongategroove on said lower surface of said upper element and a complementaryelongate ridge or elongate groove on said expansion member, saidcomplementary ridge and groove being engageable upon slidable receipt ofsaid expansion member between said upper element and said lower element.5. The device of claim 4, wherein said complementary ridge and groovedefine a dovetail configuration engageable upon slidable receipt of saidexpansion member between said upper element and said lower element. 6.The device of claim 3, wherein, said lower surface of said upper elementincludes a beveled surface.
 7. The device of claim 6, wherein saidexpansion member includes thereon a second beveled surface axiallyspaced from said beveled lifting surface and a portion between andinterconnecting said beveled lifting surface and said second beveledsurface.
 8. The device of claim 7, wherein said beveled lifting surfaceand said second beveled surface are inclined in the same direction alongthe first direction.
 9. The device of claim 1, further comprisingcomplementary detents on said upper element and said expansion memberengageable upon slidable receipt of said expansion member between saidupper element and said lower element to limit axial travel of saidexpansion member relative to said upper element.
 10. The device of claim6, wherein a detent on one of said upper element or said expansionmember defines a cylindrical projection along the axial direction andwherein the other of said upper element or said expansion member definesa cylindrical recess along the axial direction for slidable receipt ofsaid cylindrical projection therein